A wireless communication system such as LTE (Long Term Evolution) standardized by 3GPP (Third Generation Partnership Project) assumes that a plurality of base stations are located. Each base station used for the wireless communication system communicates with terminals (mobile stations) in a communication area (referred to as a cell below) of each base station. Further, a base station can divide a cell into a plurality of regions when an antenna has directionality. These divided regions are referred to as sector cells. Cells described below include not only normal cells but also sector cells.
According to LTE, the same communication band is usually used between neighboring cells. Hence, a terminal (referred to as an edge terminal below) positioned at a boundary between cells receives a strong interference from a neighboring cell irrespectively of in uplink or in downlink. To deal with such a problem, an interference management technique which is called ICIC (Inter Cell Interference Coordination) and suppresses an interference between neighboring cells by setting a priority band which enables a terminal in a corresponding cell to preferentially perform communication, and, in each cell, limiting allocation radio resources of a priority band of a neighboring cell for a terminal is known. It is conceived that radio resources are limited by excluding a priority band from an allocation target or reducing transmission power of this priority band when the priority band is notified from the neighboring cell.
As a method of setting a priority band, a technique which is called FFR (Fractional Frequency Reuse) and performs fractional frequency reuse such that a priority band does not overlap between cells is known (Non-Patent Literature 1). Further, as a priority band notifying method, LOAD INFORMATION is standardized according to LTE. For example, RNTP (Relative Narrowband TX Power) is defined in downlink of LTE, and HIT (High Interference Indication) is defined in uplink (Non-Patent Literature 2).
Further, as a counter measure for an increase in a traffic amount in recent years, a heterogeneous network in which cells of various sizes are provided by introducing base stations (small cell base stations) of low transmission power in hot spots in addition to conventional macro base stations in a mixed fashion is gaining attention. However, a cell boundary area expands as the number of cells increases, and therefore an inter-cell interference is regarded as a problem.
According to 3GPP Release 10, eICIC (enhanced ICIC) has been studied as an interference management technique, and an ABS (Almost Blank Subframe) has been standardized (Non-Patent Literature 3). eICIC is also referred to as time domain ICIC, and a base station which has set ABSs stops transmission in the ABSs through a control channel (PDCCH: Physical Downlink Control Channel) and a data channel (PDSCH: Physical Downlink Shared Channel) in downlink. A subframe is a radio resource allocation unit time. Thus, the SINR of a terminal in a neighboring cell substantially improves in the ABS, and an increase in throughputs of terminals is expected.